Heavy hydrocarbon feedstocks such as residual petroleum oil fractions and synthetic crude oils from coal usually contain a large amount of sulfur-containing organic contaminants, e.g., a sulfur content in excess of 1%. The organic sulfur compounds are in the form of mercaptans, and aliphatic and cyclic thioethers and thiophenes. Some of the sulfur compounds are readily removed by simple methods of treatment, such as extraction with solvents.
The thiophene type sulfur compounds are difficult to remove except by intensive methods which concurrently destroy or alter desirable hydrocarbonaceous components of the feedstock. The use of drastic conditions utilizing prior art procedures, such as air oxidation, causes the formation of extensive amounts of resins and coke.
Various approaches to the removal of sulfur-containing organic compounds are disclosed in the prior art. U.S. Pat. No. 2,114,852 proposes a process for removal of thiophene and alkylthiophene compounds from hydrocarbon feedstock which involves distilling the feedstock in the presence of a polar solvent which preferentially dissolves sulfur compounds. The distillation residue which contains substantially all of the sulfur and a major portion of the aromatics is subjected to a desulfurization treatment, such as selective hydrogenation or oxidation. The resultant desulfurized residue fraction is then blended with the distillate fraction which was previously separated in the distillation step.
U.S. Pat. No. 3,565,793 describes a two-step process for reducing the content of thiophene sulfur compounds of heavy hydrocarbon oils. In a first step, the oil feedstock is contacted with a peroxide oxidant in the presence of a Group IV-B, Group V-B or Group VI-B metal. In a second step, the peroxide-treated feedstock is subjected to base treatment (e.g., sodium hydroxide) or thermal treatment.
There remains a need for an economically feasible processing method for desulfurization of heavy hydrocarbon oil feedstocks which contain refractory sulfur compounds such as thiophenic derivatives.
Accordingly, it is a main object of this invention to provide a one-step process for desulfurization of hydrocarbonaceous oil feedstock.
It is another object of this invention to provide an efficient method for reducing the thiophenic sulfur content of heavy hydrocarbon mixtures such as residual petroleum oil fractions and coal-derived synthetic crude oils.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.